1. Field of the Invention
The invention relates to a method and an apparatus for checking the functioning of a pressure-operated actuating element in an internal combustion engine.
2. Related Art
DE 33 06 484 A1 discloses an internal combustion engine with an exhaust turbocharger, the turbine of which, which is located in the exhaust line of the internal combustion engine, drives a compressor arranged in the intake duct for the purpose of increasing the intake pressure. To heat an exhaust catalyst mounted in the exhaust line downstream of the turbine to its operating temperature as quickly as possible, the turbine can be bypassed by means of a bypass passage which can be opened and closed by a pressure-dependent actuator. When the bypass passage is open, some of the hot exhaust gasses flow directly to the catalyst, bypassing the turbine, and heat it quickly to its operating temperature, thereby reducing pollutant emissions after a cold start.
The actuator that opens and closes the bypass passage comprises a spring-loaded diaphragm in a housing with a pressure chamber supplied via a pressure line. If the pressure chamber is subjected to the reduced pressure that prevails, for example, in the intake manifold at idle when the internal combustion engine is started, the diaphragm and an actuating rod connected to the diaphragm are displaced, the bypass passage thereby being opened and the exhaust gas passed directly to the catalyst.
In the event of a leak in the pressure line that supplies the pressure chamber of the actuator, the pressure chamber is not supplied with the reduced pressure required to open the bypass passage but, instead, is subjected to ambient pressure, with the result that the bypass passage remains closed and the useful exergy of the exhaust gas is used to drive the turbine but not to heat the catalyst directly. If the catalyst is below its operating temperature, larger quantities of unpurified exhaust gas are then emitted.